Spin drying apparatus

ABSTRACT

A spin drying apparatus for drying semiconductor wafers wherein the wafers are contacted only at the edge thereof by a plurality of radially extending arms and wherein means is provided for preventing the generation of turbulent air flow by the fan-like effect of the rotation of the arms during the spin drying step and the recontamination of already cleaned and dried wafer surfaces by contaminants stirred up by the operation of the spin drying apparatus itself.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to spin drying apparatus for dryingplate-like or wafer-like elements, such as semiconductor wafers, duringthe fabrication of semiconductor components. Wafers used for themanufacture of integrated circuits are subjected to a plurality offabrication steps including the steps of etching, coating, doping,plating, etc. until the desired multilayered configuration is achieved.After many of the steps, it is desirable to clean the wafer in order toremove contaminants and other particles generated during the previousoperation to prepare the wafer for the following operations. The wafersmust be cleaned, often on both sides, generally employing a liquidcleaner. After the cleaning step the wafer must be dried in a mannerwhich does not leave contaminants on the surface of the wafer. Thecleanliness requirements for semiconductor wafers is such that evenfilms or stains generated by the evaporation of the cleaning fluid canbe deleterious.

Heretofore centrifugal drying of wafers has been considered the optimalmethod of drying semiconductor wafers because the centrifugal forcehelsp to overcome the surface tension and the resultant clinging ofmoisture around the edge of a wafer that can result from other forms ofdrying. Generally, spin drying has been accomplished in the prior art bya vacuum chuck which grips the wafer on the lower face thereof. It hasbeen found that holding the wafer in this manner results in staining ofthat face of the wafer because the liquid trapped between the chuck andthe wafer which either cannot be removed or, during spinning, leaks outfrom the chuck and is dried as its spreads over the wafer face leavingstains which are unacceptable.

Further, it has been found that the increasing wafer sizes now beingutilized to improve semiconductor production efficiency are increasinglydifficult to safely hold with vacuum chucks. Any imbalance with largerwafers quickly generate forces which overcome the vacuum force,resulting in the destruction of the wafer as it is flung from the chuck.

One solution for this problem has been to use a spin dryer arranged togrip the edge of the wafer during spinning. A representative type ofspin dryer employing edge gripping is disclosed in IBM TechnicalDisclosure Bulletin, Vol. 18, No. 6 of November 1975 at pages 1979 and1980. This device includes a plurality of radial arms extendingoutwardly from a central shaft which is coupled to a drive means forimparting spinning motion to the arms and a wafer held thereby. However,it has been found that with spin dryers of this type, employing radiallyextending arms to support the wafer at the edge thereof, the armsgenerates sufficient turbulent air flow that particulate contaminants(solid or liquid) may be picked up by the turbulent air and redepositedupon the cleaned and/or dried surface of the wafer. As the complexity ofsemiconductor chips increases, along with an ever-decreasing size forthe respective components thereon, it becomes more and more important toensure that the wafers are not only adequately cleaned and dried but areprotected against recontamination by contaminants anywhere during thecleaning and drying cycle. It will thus be apparent that therecontamination of already cleaned and dried wafer surfaces bycontaminants stirred up by the operation of the spin drying apparatusitself can be extremely unsatisfactory, reducing the yield of thesemiconductor devices.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a spin drying apparatus fordrying semiconductor wafers wherein the wafers are contacted only at theedge thereof by a plurality of radially extending arms and wherein meansis provided for preventing the generation of a fan-like effect from therotation of the arms during the spin drying step.

According to one aspect of the present invention, spin drying apparatusis provided for drying a plate-like element, such as a semiconductorwafer, which apparatus comprises a shaft arranged for rotary motionhaving a drive motor at one end and a rotating head assembly at theother end. The head assembly comprises a head element arranged coaxiallyat the end of the shaft, which assembly has a plurality of radial armsextending outwardly therefrom. A plurality of movable arms are pivotallyconnected one to each of the radial arms, and each have a plate-engagingportion. A biasing means is provided for biasing the plate-engagingportions of the movable arms to a plate-engaging position, and means isprovided for moving the movable arms against the force of the biasingmeans to selectively move the plate-engaging portions from theplate-engaging position. A containment means closely surrounds theradially extending arms and includes a cover element for substantiallyeliminating the generation of air flow around the plate-like element bythe rotation of said radially extending arms.

According to another aspect of the present invention, spin dryingapparatus is provided for drying a semiconductor wafer and comprises avertical hollow shaft, arranged for rotary motion and having a drivemotor at the lower end and a rotating head assembly at the upper endthereof. The head assembly includes a hollow head element coaxiallyarranged at the upper end of the hollow shaft and a plurality of pairsof spaced radial arms extending outwardly therefrom. A plurality ofT-shaped arms are pivotally connected, one between each pair of arms atthe outer ends thereof. Each of the T-shaped arms has an axiallyextending wafer-engaging leg portion and another leg portion extendingradially between the pairs of radial arms into said head element. Anactuating means is provided which includes an actuator rod disposedcoaxially within the hollow shaft, as well as means in the head elementfor engaging the inner ends of the radially extending portions of theT-shaped arms. Means is provided for biasing the actuating meanscoaxially of the shaft towards the motor to move the wafer-engaging legportions toward the center of the head assembly to a wafer-engagingposition. Pin means is disposed through the lower end of the actuatorrod, which pin means extends outwardly through the shaft and is attachedto a collar which is engageable by a fork means disposed about theshaft. An actuator means is arranged to move the fork axially of theshaft to engage the collar and to move the actuating means upwardlyagainst the force of the biasing means, thereby moving thewafer-engaging leg portions outwardly from the wafer-engaging position.A first containment means peripherally surrounds the rotating headassembly and has an open upper end with a diameter greater than thediameter of the rotating head assembly, This containment means has adownwardly and outwardly sloping intermediate portion adjacent thewafer-engaging leg portion of the T-shaped arms and a drain means isdisposed in the lower portion thereof. A second containment means isclosely and stationarily disposed about the rotating arms and is spacedinwardly from the lower portion of the first containment means. Thesecond containment means terminates at an upper end just above thepivotal connection between the arms of the head assembly. A coverelement is provided for the second containment means which is connectedto and extends from the center of the head assembly outwardly beyond theaxially extending wafer-engaging leg portions of the T-shaped arms andterminates in close proximity to the upper end of the second containmentmeans. The second containment means and the cover element substantiallyprevent air flow around the wafer which would otherwise have beengenerated by the rotation of the head assembly. The T-shaped arms areprovided with counterweights disposed on the opposite side of thepivotal connections from the wafer-engaging leg portions which provide acentrifugal force upon rotation of the head assembly that substantiallyequals or slightly exceeds the centrifugal force on the wafer-engagingleg portions during rotation. Thus, the centrifugal force of thecounterweights tends to cause the wafer-engaging leg portions to gripthe plate member. Means is also provided for elevating the rotating headassembly to a position wherein the wafer-engaging leg portions aredisposed above the open upper end of the first containment means, and afirst pair of nozzle means are arranged for directing a liquid onto bothsurfaces of the wafer during a first portion of the spin cycle while asecond pair of nozzle means direct an inert gas onto both surfaces ofthe wafer during a second portion of the spin cycle.

Various means for practicing the invention and other features andadvantages thereof will be apparent from the following detaileddescription of illustrative preferred embodiments of the invention,reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a spin dryer according to the presentinvention; and

FIG. 2 is an elevation view, partly in section, taken along line 2--2 ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2 a preferred embodiment of the spin dryerapparatus is illustrated. The spin dryer comprises a rotating headassembly 130 disposed at the upper end of a substantially verticalhollow rotatable shaft 126. The rotating head assembly 130 includes asubstantially cylindrical hollow head member 160 which is connected atthe upper end of the shaft 126, and is provided with a plurality ofpairs of spaced radially arms 124 extending outwardly therefrom. Aplurality of T-shaped arms 122 are pivotally mounted at 123 between eachpair of radial arms 124. Each of the T-shaped arms comprises an axiallyextending wafer-engaging leg portion having a wafer-engaging tip 125 atthe outer end thereof, and a radially extending leg portion whichextends into the head element 160. The wafer-engaging tip 125 at theouter end of the axially extending portion of the T-shaped arm isarranged to engage only the edge of a wafer to hold it in position forspin drying.

The shaft 126 is driven by a stepper motor 128 connected thereto bycoupling 129 at the lower end thereof. The shaft 126 is provided with acentral bore through which extends an actuator rod 162. The rod 162 hasan enlarged upper end portion 164 within the cavity of head member 160.The end portion 164 is provided with an annular recess 166 which engageswith the inner ends 168 of the radial portion of T-shaped arms 122. Abiasing means, such as compression spring 170, is disposed around theupper end of rod 162 within an enlarged bore 172 in the upper end of theshaft 126. Spring 170 is compressed between a shoulder 174 at the upperend, and a collar 176 at the lower end connected to rod 162. Thus,spring 170 exerts a downward force on rod 162, to downwardly rotate thehorizontal, radial portions of T-shaped arms 122, thereby drawing thewafer-engaging tips 125 toward the center of the head assembly into thewafer-engaging position. The lower end of the actuator rod 162 extendsto the lower end of shaft 126 and terminates in sliding engagement witha bushing 178. Just above the lower end of rod 162, shaft 126 isprovided with a pair of diametrically opposite slots 180 through thewall thereof. A horizontal pin 182 is connected through the rod 162 atthis point and extends outwardly through the slots 180 in shaft 126 andconnects to a collar 208.

Actuating means 184, either a solenoid or a pneumatic or hydrauliccylinder, is disposed on the far side of shaft 126 as illustrated inFIG. 2, with an operating shaft (not shown) extending upwardly therefromparallel with shaft 126. At the upper end of the actuator shaft a fork186 is provided having arms which extend around either side of shaft 126just below collar 208. Upon operation of actuator 184, the fork israised into engagement with collar 208, lifting rod 162 within shaft126. As the upper end portion 164 is raised, the radially extending legportions of T-shaped arms 122 are pivoted upwardly whereby thewafer-engaging tips 125 at the upper ends of the axially extending legportions of arms 122 are rotated outwardly, thereby releasing their gripon a wafer, or in anticipation of the insertion of a new wafer into thespinner apparatus. When the actuator 184 is de-energized, the fork 186is lowered, disengaging collar 208 and permitting spring 170 to forcethe rod 162 down, rotating the radially extending leg portions of arms122 about the pivots 123 whereby the wafer-engaging tips 125 are againin wafer-engaging position.

The portions 127 of arms 122 below the pivot 123 are carefully designedto counterbalance and counteract any tendency of the upper portions ofthe arms to be pulled outward by centrifugal force during the spinningoperation, with the possible resultant reduction in force gripping thewafer. Preferably the counterweights are so configured that thecentrifugal force acting on the counterweight portion substantiallyequals or is slightly greater than the centrifugal force on thewafer-engaging tips 125, whereby the centrifugal force of thecounterweight tends to cause the wafer-engaging tips to grip the waferwith at least as much, or slightly greater force than that provided bythe spring 170 alone.

The spinner head assembly 130 is surrounded by a first containment meanscomprising a stationary cylindrical collector bowl 132 which has an openupper end with a diameter sufficiently greater than the diameter of therotating head assembly that it may be moved upwardly therethrough toreceive and discharge wafers, in a manner to be described hereinbelow.The cylindrical collector bowl 132 is provided with a downwardly andoutwardly sloping intermediate portion 133 adjacent the wafer-engagingtips 125 of the T-shaped arms. The bowl is arranged to confine anymoisture centrifugally removed from the wafer and to prevent its escapeinto the remainder of the apparatus surrounding the spin dryer, orredeposition onto the wafer surface. Thus any particles, solid orliquid, which are centrifugally discharged from a surface of the waferstrike the sloping shoulder portion 133 of the bowl and are deflecteddownwardly to the bottom of the collector bowl where they are removed bya suitable drain, not shown, which is provided in the bottom of thecontainment means.

As noted above, it has been found that with centrifugal spin dryers ofthe type disclosed herein, utilizing radial arms which grip the edges ofthe wafers, that problems have been encountered because of the air flowgenerated by the centrifugal pumping action of the rotating radial arms.It has been found that this air flow results in a turbulence around thewafer which entrains particulate liquid and/or solid material which maythen be redeposited upon the wafer surface. With the present inventionsuch air pumping and turbulent air flow is substantially eliminated by asecond containment means comprising a stationary inner cylindricalshield member 200 which is disposed about the radially extending arms ofthe head assembly. The shield member is mounted to the stationaryhousing 206 for shaft 126 and is spaced inwardly from the lower portionof the cylindrical collector bowl 132. The upper end of the cylindricalshield member terminates just above the pivotal connection 123 betweenthe radial arms 124 and the T-shaped arms 122. A cover element 202 forthe second containment means is mounted on the head assembly 160 andextends from the center thereof outwardly beyond the axially extendingwafer-engaging leg portions of the T-shaped arms and terminates in closeproximity to the upper end of the shield member 200. The cover element202 is arranged to rotate with the head assembly. As illustrated, thecover element 202 is provided with a sloping outer periphery and isprovided with openings around the axially extending leg portions largeenough to permit movement thereof for engaging and disengaging a wafer.

The entire spinner assembly, including the motor 128 is arranged to belifted by a pneumatic or hydraulic cylinder 134 to lift thewafer-engaging tips 125 above the top of the collector bowl 132 forreceiving and discharging wafers from the spin dryer apparatus. The spindryer apparatus is supported and guided for a vertical movement by apair of vertical guide rods 190. Two pair of bearing blocks 192 and 194extend from the side of the spinner assembly and are provided withbearings which ride on the rods 190. The cylinder 134 is disposedbetween the rods and is connected by a bracket 196 to the side of thespinner assembly. The upper end of the piston rod (hidden behind rod190) is fixed to the mounting frame for the spinner assembly. Thus, whenthe cylinder is actuated it is drawn up the piston rod, carrying thespinner assembly with it until the wafer engaging tips 125 reach theposition illustrated in phantom, above the top edge of the collectorbowl, where it is accessible to a wafer transfer mechanism for transfereither to or from the spin drying assembly.

Two pairs of spray nozzles 136, 138 and 139, 140 are provided to sprayboth surfaces of the wafer. The first pair of nozzles 136 and 138 arearranged to spray water onto both surfaces of the wafer to provide afinal rinse before the drying cycle. The second pair of nozzles 139 and140 spray both surfaces with an inert gas such as nitrogen to assist inthe drying during the spin drying of the wafer. In a preferredoperational cycle, the wafer is first spun at a slow speed while wateris sprayed from nozzles 136 and 138 for a sufficient time to wash thewafer surface and then the speed of the motor is increased tocentrifugally dry the wafer surfaces with the inert gas provided bynozzles 139 and 140 assisting in the drying process.

It will thus be seen that the present invention provides a spin dryingapparatus which provides the advantages of gripping the wafer at theedges only and yet prevents the problem of recontamination by air pumpedby the rotating radial arms.

The control system for the spin dryer takes advantage of the use ofstepper motor 128 to control the spin cycle as well as the stoppingposition of the wafer-engaging arms. Thus, the stop position of therotating head may be selected so that the wafer-engaging arms do notinterfere with the wafer transfer mechanism transferring wafers to andfrom the spin drying mechanism.

The invention has been described with reference to specific embodimentsand variations, but it should be apparent that other modifications andvariations can be made within the spirit and scope of the invention,which is defined by the following claims.

What is claimed is:
 1. Spin drying apparatus for drying a plate-likeelement, said apparatus comprising a shaft arranged for rotary motionand having a drive motor at one end and a rotating head assembly at theother end thereof,said head assembly comprising a head element coaxiallyarranged at said other end of said shaft and having a plurality ofradial arms extending outwardly therefrom, a plurality of movable armspivotally connected one to each of said radial arms and having aplate-engaging portion, biasing means for biasing said plate-engagingportions of said movable arms to a plate-engaging position, means formoving said movable arms against the force of said biasing means to movesaid plate-engaging portions thereof from said plate-engaging position,and containment means closely surrounding said radially extending armsincluding a cover element for substantially eliminating the generationof air flow around said plate-like element by the rotation of saidradially extending arms.
 2. The invention according to claim 1 whereinsaid movable arms are substantially T-shaped.
 3. The invention accordingto claim 2 wherein each of said T-shaped arms have a first, generallyaxially extending leg portion and a second, generally radially extendingleg portion, and wherein said axially extending-leg portions extendthrough said containment cover means.
 4. The invention according toclaim 3 wherein said movable arm is pivotally connected to said radialarm at the juncture of said axially extending leg portion and saidradially extending leg portion.
 5. The invention according to claim 3wherein said axially extending leg portions of said movable armsincludes said plate-engaging portions.
 6. The invention according toclaim 3 wherein said T-shaped arms include counterweights disposed onthe opposite side of said pivotal connections from said axiallyextending leg portions, said counterweights providing a centrifugalforce upon rotation of said head assembly that substantially equals orslightly exceeds the centrifugal force on said axially extending legportions during rotation whereby the centrifugal force of saidcounterweights tends to cause the axially extending leg portions to gripsaid plate-like element.
 7. Spin drying apparatus for drying aplate-like element, said apparatus comprising a shaft arranged forrotary motion and having a drive motor at one end and a rotating headassembly at the other end thereof,said head assembly comprising a headelement coaxially arranged at said other end of said shaft and having aplurality of radial arms extending outwardly therefrom, a plurality ofT-shaped arms pivotally connected one to each of said radial arms, saidT-shaped arms each having an axially extending plate-engaging legportion, and a radially extending leg portion that extends into saidhead element, actuating means including an actuator rod disposed withinsaid shaft and means in said head element for engaging the inner ends ofsaid T-shaped arms, biasing means for biasing said actuating meanstowards said motor to move said plate-engaging leg portions of saidT-shaped arms to a plate-engaging position, means for moving saidactuating means against the force of said biasing means to move saidplate-engaging leg portions from said plate-engaging position, firstcontainment means surrounding said rotating head assembly and having anopen upper end, said first containment means having a downwardly andoutwardly sloping intermediate portion adjacent said plate-engaging legportion of said T-shaped arms, second containment means closely andstationarily disposed about said rotating arms and spaced inwardly fromthe lower portion of said first containment means, said secondcontainment means terminating at an upper end just above said pivotalconnection between said arms, a cover element for said secondcontainment means connected to and extending from said head assemblyoutwardly beyond the axially extending plate-engaging leg portions ofsaid T-shaped arms and terminating in close proximity to the upper endof said second containment means whereby said second containment meansand said cover element substantially eliminate the generation of airflow around said plate-like element by the rotation of said headassembly, and means for elevating said rotating head assembly to aposition wherein said plate-engaging leg portions are disposed above theopen upper end of said first containment means.
 8. The inventionaccording to claim 7 wherein said T-shaped arms include counterweightsdisposed on the opposite side of said pivotal connections from saidaxially extending leg portions, said counterweights providing acentrifugal force upon rotation of said head assembly that substantiallyequals or slightly exceeds the centrifugal force on said axiallyextending leg portions during rotation whereby the centrifugal force ofsaid counterweights tends to cause the axially extending leg portions togrip said plate-like element.
 9. Spin drying apparatus for drying asemiconductor wafer, said apparatus comprising a vertical hollow shaftarranged for rotary motion and having a drive motor at the lower end anda rotating head assembly at the upper end thereof,said head assemblycomprising a hollow head element coaxially arranged at the upper end ofsaid hollow shaft and having a plurality of pairs of spaced radial armsextending outwardly therefrom, a plurality of T-shaped arms disposed onebetween each pair of arms and pivotally connected to the outer endsthereof, said T-shaped arms each having an axially extendingwafer-engaging leg portion, the other leg of each of said T-shaped armsextending radially between said pairs of said radial arms into said headelement, actuating means including an actuator rod disposed coaxiallywithin said hollow shaft and means in said head element for engaging theinner ends of said T-shaped arms, biasing means for biasing saidactuating means coaxially of said shaft towards said motor to move saidwafer-engaging leg portions toward the center of said head assembly to awafer-engaging position, pin means disposed through the lower end ofsaid actuator rod and extending outwardly through said shaft andconnected to a collar, fork means disposed about said shaft and arrangedto selectively engage said collar, actuator means arranged to move saidfork axially of said shaft to engage said collar and to move saidactuating means upwardly against the force of said biasing means therebymoving said wafer-engaging leg portions outwardly from saidwafer-engaging position, first containment means peripherallysurrounding said rotating head assembly and having an open upper endwith a diameter greater than the diameter of said rotating headassembly, said first containment means having a downwardly and outwardlysloping intermediate portion adjacent said wafer-engaging leg portion ofsaid T-shaped arms, drain means disposed in the lower portion said firstcontainment means, second containment means closely and stationarilydisposed about said rotating arms and spaced inwardly from the lowerportion of said first containment means, said second containment meansterminating at an upper end just above said pivotal connection betweensaid arms, a cover element for said second containment means connectedto and extending from the center of said head assembly outwardly beyondthe axially extending wafer-engaging leg portions of said T-shaped armsand terminating in close proximity to the upper end of said secondcontainment means whereby said second containment means and said coverelement substantially prevent air flow around said wafer generated bythe rotation of said head assembly, said T-shaped arms being providedwith counterweights disposed on the opposite side of said pivotalconnections from said wafer-engaging leg portions, said counterweightsproviding a centrifugal force upon rotation of said head assembly thatsubstantially equals or slightly exceeds the centrifugal force on saidwafer-engaging leg portions during rotation whereby the centrifugalforce of said counterweights tends to cause said wafer-engaging legportions to grip said plate member, means for elevating said rotatinghead assembly to a position wherein said wafer-engaging leg portions aredisposed above the open upper end of said first containment means, and afirst pair of nozzle means for directing a liquid onto both surfaces ofsaid wafer during a first portion of the spin cycle, and a second pairof nozzle means for directing an inert gas onto both surfaces of saidwafer during a second portion of the spin cycle.